(This version of the December 7th story corrects spelling of first name to Erik (not Eric) in paragraph 21): (This version of the December 7th story corrects spelling of first name to Erik (not Eric) in paragraph 21) LONDON (Reuters) - Bitcoin’s value has plunged by three-quarters this year, sending the original and biggest cryptocurrency back to levels not seen before its bubble. And price isn’t the only aspect of trading that has changed.